Updated Dockerfile for flask app

Signed-off-by: Damanpreet Singh <daman.4880@gmail.com>

flask/app/Dockerfile

@@ -1,5 +1,6 @@
 FROM python:3.7-alpine 
 WORKDIR /app 
+COPY requirements.txt /app
 RUN pip3 install -r requirements.txt 
 COPY . /app 
 ENTRYPOINT ["python3"]